1. Field of the Invention
The present invention relates to an outer retainer for a one-way clutch which is used in an automatic transmission, or the like, of a vehicle.
2. Related Background Art
In an automatic transmission or the like of a vehicle, a one-way clutch for transmitting a rotation force on a driving side in one direction only and not transmitting the force in an opposite direction is used.
A conventional one-way clutch of a sprag type is comprised of an inner race and an outer race which are coaxially provided to rotate relatively to each other and a one-way clutch mechanism which is interposed between the inner race and the outer race. The one-way clutch mechanism is comprised of a plurality of sprags serving as torque transmitting members, a spring member for urging the sprags in a direction of engagement, cylindrical inner retainer and outer retainer for retaining the sprags and preventing their excessive inclination, and a pair of end bearings for retaining these retainers with a predetermined space therebetween so as to secure an operation of the sprags.
The outer retainer has a cylindrical portion and a flange portion which extends outward in the radial direction from one end of the cylindrical portion. The cylindrical portion is provided with a plurality of rectangular windows formed in the circumferential direction at predetermined intervals, correspondingly to the respective sprags in order to retain the sprags in the circumferential direction. The cylindrical portion and the flange portion are formed integrally.
The inner retainer has substantially the same structure as that of the outer retainer, except that a flange portion which is formed on one end in the axial direction is an inward flange which is bent inward in the radial direction.
In the one-way clutch having such a structure, when the outer race serves as a driving race for acting the rotating force on the sprags to transmit the torque, it is necessary to make proper dragging torque act between the outer retainer and the inner peripheral surface of the outer race in order to securely transmit, even if a sudden action is applied on the outer race, the action to the sprags.
As a means for obtaining such a dragging torque, Japanese Utility Model Application Laid-Open No. 62-188632 discloses that the entire outer retainer including the outward flange is formed in an elliptical shape, and the flange portion on the outer side and the inner peripheral surface of the outer ring are brought into contact at both ends in the major axis direction of this ellipse. With this structure, a necessary dragging torque is obtained.
In such a conventional outer retainer, the diameter in the major axis direction of the outer retainer taking an elliptic shape is formed to be slightly larger than the inner diameter of the outer race. For this reason, in a state where the outer retainer is attached to the inner peripheral surface of the outer race, the outer retainer is secured to the inner peripheral surface of the outer race by a spring action which is caused by distortion of the entire outer retainer.
Japanese Utility Model Application Laid-Open No. 06-22630 discloses an outer retainer which is formed in an elliptical shape, in which a cut-away portion is formed in a part of the flange portion in the circumferential direction, so that a spring property of the entire retainer can be easily obtained.
As described above, in the conventional elliptically-formed outer retainer, since the flange portion and the inner peripheral surface of the outer race are brought into contact at both ends of the elliptic form in the major axis direction thereof, the contact with the inner peripheral surface of the outer race is two-point contact. Conventionally, the outer retainer is formed in an elliptic form because the primary object thereof is to obtain a dragging torque with respect to the inner peripheral surface of the outer race. So the contact at two points with the inner peripheral surface of the outer race has no special problem.
However, in a state that the outer retainer is attached on the inner peripheral surface of the outer race, assuming that the flange portion of the outer retainer serves as means for preventing the outer retainer from falling out of the inner peripheral surface of the outer race in the axial direction, the posture of the outer retainer is ill-balanced if the flange portion is in contact with the inner peripheral surface of the outer race only at two points. That is, since the outer retainer is supported to the inner peripheral surface of the outer race at two points, the posture of the outer retainer is unstable.
Also, when the flange portion is formed with a cut-away part, as in the retainer disclosed in the Japanese Utility Model Application Laid-Open No. 06-22630, since the retainer is produced by press-working, the life of the pressing machine or a constituents parts thereof such as a punch also greatly affects the cost. Moreover, the pressing process itself becomes complicated, thereby further increasing the cost.
In assembling the outer retainer, the outer retainer is flexed to be inserted into the inner peripheral surface of the outer race. However, if a cut-away part is formed in the flange portion, the rigidity of the retainer in the circumferential direction becomes low so that the retainer may be flexed more than necessary. As a result, it is feared that the strength of the outer retainer itself may be lowered.
On the other hand, if there is a partial cut-away part at the flange portion, an edge of the flange would cause the metal mold to chip. As a result, the thermal processing may become difficult.